The Human Factor: The Two Challenge Rule
As I was talking with Dr. Martin Smith about the research he and his associates at Presage Group were doing on unstable approaches, he commented that visual approaches “were a little more seductive than instrument approaches in terms of continuing with an approach that is unstable.” Dr. Smith said even though all of the participants in the study were professional pilots and most were flying scheduled short-haul passenger service under instrument flight rules, 80 percent of the unstable approaches reported in the study occurred during visual meteorological conditions.
The Presage data shows pilots flying an approach in VMC are more likely to be flying the airplane manually, seem less aware of operational and environmental threats, are less likely to view those threats as unmanageable, are less likely to rely on expert knowledge of instruments and procedures and have lower confidence in their companies’ go-around policies. As Dr. Smith said: “That’s some seduction! It’s almost like they’re hand-flying a Cherokee 140 on a CAVU summer day with not a worry in the world.” Dr. Smith worried that due to the normalization of deviance mentioned in my previous article, these nonprescribed, deviant behaviors may have become the accepted way to conduct VMC approaches within the industry.
This made perfect sense to me and was illustrated by my own experience that I related last month about an ILS approach in a Learjet to Houston’s William P. Hobby Airport at 4 a.m. After considering Dr. Smith’s comments, I realized my approach was no more stable after we broke out of the clouds than it was a few seconds before when we were still in the clouds. The only difference was that I was now flying an unstable approach visually rather than on the instruments. Like the pilots in the study, once I was in VMC, I had more confidence in my ability to compensate for the unstable approach and disregarded standard operating procedures that required a go-around in that situation.
The Sirens’ Song
My experience illustrates the powerful “sirens’ song” that tempts us into continuing an approach that is unstable, especially when operating in VMC. The sirens were depicted as enchanting, partly human creatures in Greek mythology that enticed sailors to crash their ships with their alluring music. Their song has been described as lulling the listener into a fatal lethargy with an appeal that is hard to resist but if heeded will lead to a bad outcome. It is amazing how well this description fits what happens to a pilot on an unstable approach. The sirens’ song tells us if we just continue the approach a little bit farther, we will be able to get things back under control. This leads to a fatal lethargy in which the pilot does not take decisive action to respond to the obvious danger but continues the unstable approach, hoping everything will fall into place. The bad outcome can be anything from a hard landing to a fatal crash.
Odysseus instructed his sailors to put beeswax in their ears and then tie him firmly to the mast so he could safely listen to the sirens’ song without being able to jump overboard to try to swim to the shore. While rope or beeswax might not be of much help to a pilot, something called the Two Challenge Rule could be very useful in overcoming the temptation to continue an unstable approach, hoping that everything will turn out well in the end.
The Two Challenge Rule was developed after research and actual accidents showed approximately 25 percent of copilots would allow a captain to continue even a radically unstable approach due to the incapacitation of the captain as long as that incapacitation was not obvious. It states that the copilot or pilot not flying (PNF) would assume control of the airplane if the captain or pilot flying (PF) did not respond appropriately after two callouts. For example, if the airplane begins to descend below the glideslope, the PNF would state, “Half-dot low and increasing.” The desired response is “Correcting,” followed by the appropriate action to return to the desired flight path or configuration. If there is no response from the PF and/or the airplane continues to sink below the glideslope, the PNF would state, “One dot low and increasing.” If there was still no response or effective correction from the PF, the PNF would state, “I have the controls” and initiate a missed approach.